Triscone.pdf

Electric Field Control of the Electronic Properties of
the Interfacial LaAlO3/SrTiO3 System
STEM by L. Fitting-Kourkoutis,
D.A. Muller (Cornell)
… …
AlO2 LaO
TiO 2
SrO
(001)
Jean-Marc Triscone - University of Geneva
LaAlO 3:
band insulator
SrTiO 3:
band insulator
quantum paraelectric

… …
AlO 2
LaO
TiO 2
SrO
(001)
2D Electron Gas
..............................................................
Ahigh-mobilityelectrongasat
the LaAlO 3/SrTiO 3 heterointerface
A. Ohtomo 1,2,3 & H. Y. Hwang 1,3,4
Nature 427, 423 (2004)
1
Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 07974, USA
2
Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan
3
Japan Science and µ Technology 1000 Agency, cmKawaguchi, 332-0012, Japan
4
Department of Advanced Materials Science, University of Tokyo, Kashiwa,
2 /Vs
Chiba, 277-8651, Japan
.............................................................................................................................................................................
Polarity discontinuities at the interfaces between different crystalline
materials (heterointerfaces) can lead to nontrivial local
atomic and electronic structure, owing to the presence of dangling
bonds and incomplete atomic coordinations 1–3 . These discontinuities
often arise in naturally layered oxide structures,
such as the superconducting copper oxides and ferroelectric
titanates, as well as in artificial thin film oxide heterostructures
such as manganite tunnel junctions 4–6 . If polarity discontinuities
can be atomically controlled, unusual charge states that are
inaccessible in bulk materials could be realized. Here we have
examined a model interface between two insulating perovskite
oxides—LaAlO3 and SrTiO3—in which we control the termination
layer at the interface on an atomic scale. In the simple ionic
limit, th
two-dim
interface
whereas
tremely
low tem
odic wit
quantum
tailor lo
oxide he
An ear
the cons
Both sem
exact la
combine
Just at t
terminat
III–V alt
design i
dangling
an intim
charge-t
sequenc
phases,
accomm
charge n

… …
AlO 2
LaO
TiO 2
SrO
(001)
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H⟘
100mT
H⫽
flux of upward-propagating low-frequency waves
throughout the solar corona. These waves propagate
at speeds typical of Alfvén waves, and their
direction of propagation mirrors the measured
magnetic field direction. The waves we resolved
do not have enough energy to heat the solar
corona. We conclude that these ubiquitous waves
are indeed Alfvénic and offer the real possibility
of probing the plasma environment of the solar
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A 2D Superconducting Electron Gas
(T = 0) 60 nm d ≈ 10 nm
1196
Superconducting Interfaces Between
Insulating Oxides
N. Reyren, 1 S. Thiel, 2 A. D. Caviglia, 1 L. Fitting Kourkoutis, 3 G. Hammerl, 2 C. Richter, 2
C. W. Schneider, 2 T. Kopp, 2 A.-S. Rüetschi, 1 D. Jaccard, 1 M. Gabay, 4 D. A. Muller, 3
J.-M. Triscone, 1 J. Mannhart 2 *
At interfaces between complex oxides, electronic systems with unusual electronic properties can
be generated. We report on superconductivity in the electron gas formed at the interface between
two insulating dielectric perovskite oxides, LaAlO3 and SrTiO3. The behavior of the electron gas
is that of a two-dimensional superconductor, confined to a thin sheet at the interface. The
superconducting transition temperature of ≅ 200 millikelvin provides a strict upper limit to the
thickness of the superconducting layer of ≅ 10 nanometers.
I
npioneeringwork,itwasdemonstratedthata
highly mobile electron system can be induced
at the interface between LaAlO3 and SrTiO3 (1). The discovery of this electron gas at the
interface between two insulators has generated an
impressive amount of experimental and theoretical
work (2–8), in part because the complex
ionic structure and particular interactions found at
such an interface are expected to promote novel
1 Département de Physique de la Matière Condensée,
University of Geneva, 24 quai Ernest-Ansermet, 1211 Genève
4, Switzerland. 2 Experimental Physics VI, Center for Electronic
Correlations and Magnetism, Institute of Physics, University of
Augsburg, D-86135 Augsburg, Germany. 3 School of Applied
and Engineering Physics, Cornell University, Ithaca, NY 14853,
USA. 4 Laboratoire de Physique des Solides, Bat 510, Université
Paris-Sud 11, Centre d’Orsay, 91405 Orsay, Cedex, France.
*To whom correspondence should be addressed. E-mail:
jochen.mannhart@physik.uni-augsburg.de
Science 317, 1196 (2007)
electronic phases that are not always stable as
bulk phases (9–11). This result also generated an
intense debate on the origin of the conducting
layer, which could either be “extrinsic” and due
to oxygen vacancies in the SrTiO 3 crystal or
“intrinsic” and related to the polar nature of the
LaAlO 3 structure. In the polar scenario, a
potential develops as the LaAlO3 layer thickness
increases that may lead to an “electronic reconstruction”
above some critical thickness (5).
Another key issue concerns the ground state of
such a system; at low temperatures, a chargeordered
interface with ferromagnetic spin alignment
was predicted (4). Experimental evidence
in favor of a ferromagnetic ground state was
recently found (6). Yet, rather than ordering
magnetically, the electron system may also
condense into a superconducting state. It was
proposed that in field effect transistor config-
31 AUGUST 2007 VOL 317 SCIENCE www.sciencemag.org
by grant ATM-0541567 from
Supporting Online Materia
www.sciencemag.org/cgi/content/f
Materials and Methods
Table S1
References
Movies S1 to S4
2 April 2007; accepted 27 July 2
10.1126/science.1143304
urations, a superconduc
(2D) electron gas might
SrTiO 3 surface (12). It wa
the polarization of the SrT
the electrons on SrTiO 3 su
at high temperatures a
densate (13, 14). In this
ground state of the LaAlO
clarify whether it orders
approaches absolute zero.
vide evidence that the inve
condense into a superco
characteristics of the tra
with those of a 2D electro
Berezinskii-Kosterlitz-Th
tion (15–17). In the oxy
the observation of superc
strict upper limit to the t
conducting sheet at the La
The samples were p
LaAlO 3 layers with thick
unit cells (uc) on TiO2-ter
of SrTiO 3 single crystals (
grown by pulsed laser de
6 × 10 −5 mbar O 2,thenc
ature in 400 mbar of O2,w
step at 600°C. The fact tha
with a LaAlO3 thickness
conduct (5) was used to
(19). Without exposing t
terface to the environmen
of 100 mm and lengths o
were structured for four
as well as two-uc-thick L
erence (18).

Outline
Electric field control of superconductivity,
phase diagram
Magneto-transport and spin-orbit coupling
Superconductivity in nanostructures

The «Geneva» LaAlO3/SrTiO3 Team
Stefano Gariglio
Alexandre Fête
Daniela
Stornaiuolo
Denver
Li
Marc Gabay
(University of Paris-Sud)
Andrea Caviglia
(now in Hamburg)
in collaboration with
University of Geneva
• Alberto Morpurgo
Benjamin Sacépé
• Didier Jaccard
Gabriel Seyfarth
• Christophe Berthod
Claudia
Cancellieri
(now at PSI)
and:
• Philippe Ghosez (Liège)
• Phil Willmott (PSI)
Nicolas Reyren
(now in Paris)
• Jochen Mannhart (Stuttgart)

«Standard» LaAlO3/SrTiO3 Samples
Layer-by-layer growth
T = 800°C «standard»
P O2 = 1·10 -4 Torr
Fluence = 0.6 J/cm 2
Frequency = 1Hz
Post annealing @ 200 mbar O2
Intensity (a.u.)
16 18 20 22 24 26 28 30

Ti O 3.9 Å
TiO2-plane
Transport Properties
R sheet (Ω/)
500
400
300
200
100
~2-8×10 13 /cm 2
mobilities 100-1000 cm 2 /Vs
0
200 300 400 500 600
T (mK)

Field Effect Experiments
IS VS VD ID
SrTiO 3
VG,b

Ti O 3.9 Å
TiO2-plane
«Standard» Samples
R sheet (Ω/)
500
400
300
200
100
~2-8×10 13 /cm 2
mobilities 100-1000 cm 2 /Vs
0
200 300 400 500 600
T (mK)

A
R sheet (Ω/)
1x10 4
R Q
1x10 3
1x10 2
Modulation of SC
- 300 V
320 V
1x10
50 100 150 200 250 300 350 400
1
T (mK)
A.D. Caviglia et al, Nature 456, 625 (2008)
5
50 150 250 350 0
T (mK)
20
15
10
R Q
B
R sheet (kΩ/)

System Phase Diagram
See also C. Bell et al. PRL 103, 226802 (2009).

Weak Localization to Weak Antilocalization
Δσ /(e2 Δσ /(e /π h) 2 /π h)
1
0.4
0.2
0.5
0
-0.2
0
-0.4
-0.6
-0.5
-0.8
-1
-1.2
-4 -2 0
μ 0 H (T)
2 4
Weak localization
LAO
STO T=1.5K
-300 V
-100 V
-300 V
-50 -100 VV
-50 V
0 V
0 V
+50 V
+50 V
+100 V
A.D. Caviglia et al., Phys. Rev. Lett. 104, 126803 (2010)
Weak anti-localization
Strong spin-orbit interaction

B (T)
i,so
B (T)
el,so
m*/m* max
10
1
0.1
0.01
0.001
10
1
0.1
1
0.8
0.6
0.4
0.2
-300 -200
V (V)
-100 0 100
a)
b)
c)
WL WAL AM
T c - PRL 104
B i - PRL 104
B i - this work
B so - PRL 104
B so - this work
B so - this work
B - this work
el
0.1 1
σ (mS)
2D
1
0.8
0.6
0.4
0.2
T (K)
c
B≈1/Dτ
τso∼τel -1
Rashba spin orbit
s
m ⇤ = h2
4⇥
Bso
⇤0

M. Salluzzo et al., PRL 102, 166804 (2009)
Electronic Structure
ns=3.3 10 14 cm -2
Delugas et al., PRL 106, 166807 (2011)

Spin-orbit and Magneto-transport in // Field
B (T)
i,so
B (T)
el,so
m*/m* max
10
1
0.1
0.01
0.001
10
1
0.1
1
0.8
0.6
0.4
0.2
-300 -200
V (V)
-100 0 100
a)
b)
c)
WL WAL AM
T c - PRL 104
B i - PRL 104
B i - this work
B so - PRL 104
B so - this work
a)
B 1
so - this work
B el - this work
0.995
σ (mS)
2D
σ (mS)
2D
c)
σ (mS)
2D
0.99
0.985
0.99
0.985
Exp.
0.1
1
1
0.995
σ 2D(mS)
1.004
0.999
0.994
0.989
Theory
0 50 100 150 200 250 300
ϕ (°)
Experiment
Theory
1
7T
1.75T
3.5T
5.25T
7T
0.8
0.6
0.4
0.2
1.75T
3.5T
5.5T
T (K)
c
b)
σ 2D (mS)
σ (mS)
d)
!
2D
σ (mS)
2D
3 2 3
4 2
2.04
2.02
2
2.06
2.02
2
Exp.
7T
5.25T
3.5T
1.75T
2.04
E kF m
7T
⇤
0
Bso Bso = 4 D⇥so
⇧ Bel = 0
4 D⇥
Theory
5.5T
3.5T
1.75T
⌅WL(B = 0) Bel
0 50 100 150 200 250 300
⌅WL(B = 0)
ϕ (°)
2.06
2.03
2
m ⇤ ⌅D V
Experiment
Theory
B =0
⌅WL(B = 0) = e2
✓
⇤h
A. Fête et al. arXiv:1203.5239
Log[(1 + Bso
Bin
)(1 + 2Bso
)
Bin
1
2 ] Log[ Bel
Bin
Bso
◆
]
⇧so ⇧ 2
⇥so = ⇤2 so⇧ so ⇥ ~⇤so =2 EkF
m ⇤ = h2
4⇤ E
r Bso
⇥0
⇥0 = h
2e
D = 1
2 vF 2 ⇧
µD µ Bel
Bi

1mS
Δso=2.5 meV
a)
σ (mS)
2D
σ (mS)
2D
c)
σ (mS)
2D
a)
kx
b) c)
E (meV)
1
0.995
0.99
0.985
1
0.995
0.99
0.985
1.004
0.999
0.994
(B =0)=2
⇥
dxz
Exp.
Theory
0 50 100 150 200 250 300
ϕ (°)
0.989
0 2 4
B (T), Φ=90°
6 8
dyz
dxz
Experiment
Theory
dyz
mh ⇥ 20me
E (meV)
E Γ
B= 1 T
kx
B ⌅ =0
B Rashba ⌅ = 2
B
7T
1.75T
3.5T
5.25T
7T
1.75T
3.5T
5.5T
ext E
b)
σ 2D (mS)
σ 2D (mS)
d)
σ (mS)
2D
2.04
2.02
E (meV)
2
2.06
2.04
2.02
2
2.06
2.03
2
0 2 4
σ y=+1/2
6 8
B (T), Φ=90°
B= 0 T
Exp.
Theory
0 50 100 150 200 250 300
ϕ (°)
Experiment
Theory
σ y=-1/2
(B,⇥) ⇥
B B (B =0)=1
⇥(B,⌅ = /2)
EF
B =0
g(EF ) ⇥ J
⌅ =0 EF ⇥ E
EF E g(EF )
B =0
E dxy
EF
EF E dxz
J
7T
5.25T
3.5T
1.75T
7T
5.5T
3.5T
1.75T
g(EF )
dxz
B B= 1 T
⇤
⌅ B
B
kx
⌅ Bext (⇥(B,⌅ = /2)
⇥
Bdxz Rashba
EF
⇥(B,⌅ = 0))/⇥(B,⌅ = 0) =
1/8(⇥so/EF ) 2
A. Fête et al. arXiv:1203.5239
B
⇥so
t2g
2mS
Δso=7 meV

alues of
conducerimene
shown
D(B, )
0
2D =2
re which
lays the
, = 0)
ental re-
.5) meV
ll within
, 14].
tal oscildifferent
ero for a
se sheet
egime –
portant
g super-
ion that
e, as one
conduc-
V ,conorbitals,
e severe
f V ,the
dxz,dyz
uctivity,
and by
nce. For
interactructure
e trans-
0 2 4 6 8
B (T)
FIG. 3: (color online) Experimental and model determined
plots of 2D versus B for
0
2D =1mS and 0 2D =2mS.
Δσ (μS)
2D
20
15
10
5
0
2D-SC
0.1 1
0
2D
Are the dxz, dyz bands playing
a special role for
superconductivity?
Some Correlations
σ (mS)
7T
5.25T
3.5T
1.75T
FIG. 4: (color online) Evolution of the amplitude of the experimental
oscillations 2D ( 2D = 2D(B, = ⇡
2 )
0
2D(B, =0)) as a function of 2D ."Plus"symbolspertain
to measurements performed on an additional sample at 7 T.
for their technical assistance. This work was supported
by the Swiss National Science Foundation through the
National Center of Competence in Research, Materials
with Novel Electronic Properties, MaNEP and division
II, by the Institut Universitaire de France (MG), and the
τ (ps)
0.8
0.6
0.4
0.2
0
Ref. [13]
this work
Ref. [13]
this work
0.1 1
0
σ (mS)
2D
Signature of a spin-orbit
protected transport in the 2D
conducting sheet ?
2.5
2
1.5
1
0.5
0
e
m*/m

Conclusions
Magneto-transport and superconductivity reveal the
importance of the sub-band structure
Magneto-transport and SdH analyses display signatures of
the presence of spin orbit in the system
The gas properties are preserved in «nano-structures» - that
may reveal signatures of the SC gap